In conventional X-ray computed tomography, as shown in FIG. 1 by a solid line, a projectional distribution of X-ray is measured by an X-ray detector. The X-ray beam is projected from X-ray source a toward a tissue of body b. Then, as shown in FIG. 1 by a dotted line, X-ray source a and X-ray detector c are rotated by a desired angle .alpha. (for example 1.degree.), and at this position the X-ray beam is projected again toward the body tissue of body b, a projectional distribution of X-rays under the rotation of an angle of .alpha. is measured again and several, 60 to 360 times of, similar operations are performed. Thereafter, data provided by these many projectional distributions of X-ray are calculated by Fourier transform or a convolution method, and a tomography of the X-ray tested tissue of body b is reproduced on the basis of a result of the processing.
However, in this type of a conventional X-ray computed tomography, it is necessary to have many projectional distributions of X-ray in order to reproduce a tomogram of an X-ray analyzed tissue b, resulting in some problems as follows:
(1) Since a long period of time is needed (several seconds to several minutes) for measuring, it is not possible to reproduce a tomogram of a moving tested tissue of body b.
(2) Exposure to X-ray is at a high level, resulting in some bad effects to the tested tissue of a body when the tested or analyzed tissue b is a living thing such as a human body.
The present invention is provided to overcome these disadvantages and its object is to provide a reconstruction method of X-ray computed tomography in which a reconstruction image having a high accuracy or precision may be produced by using only a projectional distribution of X-rays as data for reconstructing a tomogram of the tissue being analyzed.